Some people refer to an angle grinder wheel as a blade because of its sharp edge. You might want to change the wheel for a coarser or finer one, depending on the job. Further, you sometimes need to change a broken or worn wheel. There are many different brands of angle grinder on the market. However, the procedure for changing the wheel on the Bosch 1357 range of angle grinders is typical.
Disconnect the angle grinder from the mains. Press and hold the spindle lock button. This prevents the spindle from rotating. This is useful because otherwise the spindle would rotate, counteracting the next step.
Turn the angle grinder over so the spindle is face up. Locate the lock nut. This sits against the wheel holding it in place. Unscrew the lock nut with the lock nut wrench. Remove the lock nut.
Remove the current wheel from the spindle. Slip the new wheel onto the spindle. Place the lock nut on top. Tighten the lock nut with the lock nut wrench. Release the spindle lock button.